Manufacture of titanium dioxide pigments



atented Nov. 9, 1943 STATS 2,333,862 I MANUFACTURE or Transmit mos HGMEN'ES tion at 01110 No Drawing. Application may 2, 1942, Serial No. M11532 7 Claims.

This invention relates to the preparation of titanium pigments, and particularly to the preparation of nuclear solutions and seed crystals and their use in the precipitation of titanium compounds by hydrolysis at elevated temperatures of sulphuric acid solutions containing titanium.

This application is a continuation-impart of our prior. and copending applications Serial Number'356fie6, filed Sept. 13, 1940 and Serial Number 377,046, filed Feb. 1, 1941.

Titanium dioxide pigments are most commonly precipitated from titanium sulphate solutions which have been prepared from the reaction product of a titanium-bearing material such as illnenite ore and sulphuric acid. The prepara-- tion or such solutions is well known in the art and has been described by Blumenfeld in U. S. latent No. 1,50%,669 and by others.

The solution obtained by leaching the digestion ss with water is first treated with suficient metallic iron to reduce all of the iron prescut to the ferrous state and then chilled to crystallize out the major portion of the iron present as the sulphate. The solution at this stage may contain around 9% to 13% of T102, and is then customarily mitted to a vacuum concentration process to bring the T102 content up to 15% to 16%.

This solution may then be hydrolyzed by boil-= ins, but it is customary to assure the presence of a nuclear material in the solution, prior to any actual precipitation of the T102 by boiling, for the pose of accelerating the rate of hydrolysis, increasing the yield and controlling the plwsical characteristics of the precipitated particles. This nuclear material may be formed in situ in the solution by dilution under rigidly controlled conditions, or added as a separately prepared seeding material.

In the prior art, titanium dioxide produced from the precipitate resulting from the hydrolysis at elevated temperatures of a crystalloidal solu- I tion of titanium in sulphuric acid in the presence of an adequate amount of colloidal T102 compound, as seeding material, after suitably washins, treating, and calcining, has been the one use modification.

In our copendlng application, Serial No. 356,6i6,

I to which this application is related, we have shown that when a specific type of titanium compound which we have termed -y-titanic acid is added to the sulphuric acid'solution or titanium ass nucleating agent, the precipitate obtained by thermal hydrolysis may be calcined to the (ill) rutile modification at temperatures between 800 C. to 1,000? C.

In said last mentioned application, 'y-titanic acid is defined as a form of hydrous titanium oxide characterized as producing upon X-ray analysis a band diffraction pattern, the bands not corresponding in position to either the characteristic position of rutile or anatase lines. The characteristic positions of the bands and lines are shown in the following table:

Bands of 'y-titanio acid Lines of Lines of anatese rutile 1. u. Inten- V (1/11 arty .i. U. A. U. 5. 83 5 3. 49 I 3. 24 3.99 10 2. 37 2. 48 8. 4G 6 1. 883 2. 29 3. 1415 2. 5 1. 695 2. 18 2. 600 Z. 5 1. 655 2. 04 2. 342 3. 5 1. 477 1. 685 2. 132 3. 5 1. 358 1. fil7 1. 8. 0 1. 334 l. 479 1. 1. 5 1. 251 1. 448 1. 9. 5 1. 161 1. 351 3. 0 1. 044 1. 240 2. 5 l. 015 1. 167 3. 5 951 1. 144 2. 5 913 1. 092 5. 0 S92 1. 5 876 6. 0 843 0. 5 .824 2.0 808 4. 0 0. 5 8. 0 2. 0 3. 0 3. 5 1 2. 6 3. 5 1

It will then be understood that in this specification andin the claims of this application the term -titanic acid is used to denote a com pound of tium so defined.

Applications Serial Nos. 356,646 and 370,486 further describe several methods by which 'y-titanic acid may be prepared.

We have found that when. 'y-titanic acid is added to an ilmenite solution as a nucleating agent prior to hydrolysis. the precipitate obtained by hydrolysis will be or the anatase crystal structune, but difier from ordinary anatase hydro from sulphate solutions in that after suile seation and washing, it calcine to rutile at temperatures between 800 C. to 1,000 0., and in this last property only bears any relationshlp to -y-titanic acid. We have further found that when a sulphuric acid solution of titanium is nucleated with anatase derived from a 'y-titanic-acid nucleated sulphuric acid solution of titanium such as an ilmenite solution, the products o1 hydolysis are identical with the nucleating agent.

We have further found that either -y-titanic acid or anatase derived by thermal hydrolysis of a 'y-titanlc acid nucleated solution of titanium sulphate such as an ilmenite sulphate solution, may be used as nucleating agents for solutions of titanium in sulphuric acid in the presence of extender pigments, and that the products of hydrolysis, upon suitable washing, treating and calcining, will be titanium extended pigments wherein the titanium dioxide component is present as the rutile crystalline form.

The treating" above referred to may be with MgO,-ZnO and their salts, and the amounts may be 0.1% to 0.5% as oxide based on TiOz.

It was not known or disclosed in the prior art that such a compound could be used as a nucleating agent for ilmenite solution to produce a product readily convertible into rutile.

Example 1.'y-titanic acid was prepared by dissolving titanium tetrachloride in twice its volume of water and slowly adding this mixture to four times its volume of 20% aqua ammonia. The precipitate was washed until the filtrate was substantially free from ammonia. The wet cake contained 30% T: in the form of v-titanic acid as established by air drying a small sample at 60 0., and showed, upon X-ray examination, the diffraction pattern typical of 'y-titanlc acid. The wet cake was redispersed in an equal weight of sulphuric acid with low heat or no heat and an amount of this dispersion equivalent'to one gram of T102 was added to 1250 grams of ilmenite solu tion containing 8.1% T102 and 19% H2804. This nucleated ilmenite solution was added to a slurry of anhydrite in water containing 235 grams CaSO4, 180 grams H2804, and 820 grams of water. The mixture was boiled four hours to complete the thermal hydrolysis of the titanium. The

solids were separated and washed until the filtrate was iron-free, dewatered and calcined two hours at 975 C. The product was a titamum extended pigment containing approximately 70% C8304 and 30% TiOz, and in which thetitanium con: tent was present substantially as rutilei Example 2.A quantity of 'y-titanic acid moist cake prepared from titanium tetrachloride solution as in Example 1 was added to ilmenite solution containing 8.1% T102 and 19% H2504 in the proportipn of one gram T102 as 'y-titanic acid to every 100 grams of TiOzin the ilmenite solution. 1250 grams of this nucleated ilmenite solution were added to 1240 grams of a calcium sulphate slurry prepared by running 10% lime slurry into 93% H2804. The calcium sulphate slurry contained 235 grams of CaSO4, and 185 grams H2804. The mixture was boiled three hours, separated, washed until the filtrate was free from ir'on, by which time the proportion of CaSOuTiO: was 70:30. The wet cake was mixed with 0.2%

The product hada tinting strength of 635, excellent whiteness and texture, and the titanium content was present as rutile.

Example 3.-A quantity of dried fluoride process hydrate prepared by contacting ammonium fiuotitanate solution with ammonia, separating and washing the precipitate, reslurrying in five times its weight of water, dewatering and air drying to 75% T102. in the form of 'y-titanic acid, was added to ilmenite solution in the proportion of one gram TiOa as v-titanic acid to 100 grams T10: in the ilmenite solution. 1250 grams or this nucleated ilmenite solution were then mixed with 1240 grams of a slurry containing 240 grams an- The mixture was boiled for three hours, dewatered, washed until the filtrate was iron-free, and dewatered. The recovery of titanium was95%, and the ratio of CaSOrzTiOz in the cake was 70:30. The cake was treated with 0.2% MgO (added as MgSO4 based on weight of total solids in the cake) and calcined for two hours at 975 C. The product was of very soft texture, tinting strength=600, and high whiteness and brightness. The titanium content was shown by X-ray examination to be rutile.

Example 4-250 grams of CaO slurry containj ing grams CaO were poured into 110 grams of 96% sulphuric acid. To this were added 3000 grams of ilmenite solution containing 8.3% TiOz and 19% H2304, and to which had been added 1 gram of TiO: as 'y-titanic acid prepared as in Example 3 for each 100 grams of TiO: in the ilmenite solution. The mixture was boiled for four hours and washed with water until the calcium sulphate was substantiall all removed. The cake, after dewatering, was calcined at 975 C. for two hours. The product was soft textured, pigmentary rutile.

Example 5.'y-titanic acid was prepared by contacting a solution of ammonium fluotitanate with excess ammonia. The precipitate was separated from the mother liquor in a filter and washed with five times its weight of water. The cake was reslurried and again washed in a similar manner and dewatered. The cake was air dried to 75% T102. 100 grams of the cake was crushed and slowly added, with agitation to 350 gramsof 30% sulphuric acid. A clear liquor resulted containing approximately 22% T102.

' ture was boiled for three hours, the precipitate dewatered, washed until the filtrate was iron- 1 free, and dewatered. The recovery of titanium ZnO (added as zinc sulphate solution) and calcined two hours at 975C.

was and the ratio of CaSOuTlOz in the cake was 70:30. The cake was treated with 0.2% MgO (added as MgSO4 solution andbased on the'weight of total solids in the cake) and calcined for three hours at 975 C. The product was of excellent texture, tinting strength=600, and high whiteness and brightness. The titanium dioxidev content was shown by X-ray examination to be rutile.

30% hydrochloric acid or twice the weight of 20% nitric acid instead of sulphuric acid may be used to redisperse the 'y-titanic acid of the wet cake in Examplb 5 with equivalent results.

While we have used calcium sulphate in the anhydrite form as the extender in the examples given, other extenders such as barium sulphate may be used. Also, the extender may be introduced after the hydrolysis of the nucleated ilmenite solution, or into the wet hydrate prior to calcination with satisfactory results, and. extenders somewhat susceptible to hot strong acid may 2,883,862 I be employed in this manner, as chalk, calcium carbonate, asbestine, micaceous. extenders, etc.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

1. The process of making an extended pigment which includes nucleating an ilmenite solution with 'y-titanic acid and hydrolyzing said solution by boiling in the presence of an extender.

, 2. The process of making a pigmentary rutile which includes nucleating an ilmenite solution with 'y-titanic acid, hydrolyzing said solution by boiling in the presence of calcium sulphate, sep

- arating the precipitate, washing out the calcium tion of titanium with q-titanic acid, adding a slurry of calcium sulphate containing sulphuric acid, and hydrolyzing said solution by boiling.

' 5. The process of making an extended pigment which includes nucleating a sulphuric acid solution of titanium with 'y-titanic acid, adding a slurry oi anhydrite containing sulphuric acid, and hydrolyzing said solution by boiling. V

6. The process of making an extended pigment which includes nucleating a sulphuric acid solutionv oi titanium with -titanic acid, hydrolyzing said solution by boiling in the presence 01 an extender, separating the precipitate, washing it free oi iron to form a wet cake, mixing with said cake a small amount oi a salt selected from the group consisting of sulphates oi. zinc and magnesium, and calcining at a temperaturenot in excess of 1.000 C.

7-. The process oi making an extended pigment,

. which includes nucleating a sulphuric acid solution ot titanium with a small portion of a sulphuric acid, dispersion ot a separated, washed and air dried precipitate produced by the action of ammonia in an ammonium fluotitanate solution, and hydrolyzing said nucleated solution by boiling in the presence or an extender,

ANDREW T. MOCORD. HAROLD F. SAUNDERS. 

